A few years
ago I produced
a cross between a young River Red Gum tree growing on our place and some
large mature Yellow Box trees.
This happened after taking seed from the vigorous young Red Gum and finding
that the resultant seedlings were about 50/50 pure River Red Gum and some
unknown box-like seedling.
the seedlings into CSIRO (Commonwealth Scientific Industrial Research
Organisation) where a eucalypt expert, Mr Ian Bruckner, confirmed that
they were hybrids, (River Red Gums hybridise readily and there is no reason
why they would not cross with E.Melliodora Yellow Box). Mr Bruckner
said that though he was 99% sure of its hybrid nature, he would nevertheless
like to further confirm after seeing the flowers of the suspected hybrids.
I am still waiting for them to flower, but their growth and interesting
behaviour seems to further confirm their E.MelliodoraXE.Camaldulensis
hybrid nature. Before I discuss their present growth habits, I will digress
and discuss why the two trees are of particular interest.
I saw representatives of CSIRO back in 1994, they told me that their work
in hybridising eucalypts mostly revolved around the softer pulpwood species.
They were concentrating on crossing species so that pulpwood plantation
farmers could grow pulpwood trees in colder areas. Admirable as this might
be, the slower growing Ironbarks and Boxwood trees are not regenerating
in their native habitat, and their timber, which is the hardest and heaviest
in the world, and which cannot be excelled for its durability and myriad
uses, from heavy construction to railway sleepers and fence posts, is
becoming more scarce, and is being replaced by shoddier products.
(Ironbark is so heavy, the early settlers found that they could not build
boats out of it, as it would sink.)
The CSIRO magazine ECOS said in 1994 about natural Boxwood woodlands in
European settlement, grassy box woodlands covered millions of hectares
between Southern Queensland and Northern Victoria. They featured eucalypt
species such as Yellow Box, Grey Box and White Box with an understorey
of kangaroo grass, wallaby grass, and snowgrass and wildflowers such as
yam daisies, donkey orchids and chocolate lilies.
Scattered trees remain, but native understorey has been eliminated from
most sites. Prober and her colleagues are studying the ecology and genetics
of remnant grassy White Box woodlands to develop a strategy for conserving
threatened woodland ecosystems. They estimate that less than 50 hectares
of the original woodlands remain intact.
species are disappearing and regeneration is not happening. Originally
growing in the more fertile valleys and woodlands rather than ridges,
they were in the way of what looked like good grazing land, and were zealously
Regrowth is subject to insect attack which kills many trees, and farmers,
who prize Boxwood for its uses as fenceposts and as a fiercely hot and
slow burning fuel, lose patience when it comes to waiting for these trees
to regrow. The average growth rate of Yellow Box is about one inch a year.
I have some naturally regenerating Yellow Box trees on my place which
in ten years dont appear to have grown at all, and some have even
been retarded in their growth by the native pests that plague them. At
their young stages of growth many regenerating Box trees are lost to pests.
They become too big and dangerous to be cultivated as park or backyard
trees. Like most eucalypts, they eventually drop branches, and these outlandishly
heavy branches are often the size of a medium tree. They are definitely
In Australia, you still pay extra for firewood that can be guaranteed
to be Yellow Box, and its very desirability as a fuel has helped in the
E. Camaldulensis, (River Red Gum) on the other hand is still the most
widespread eucalypt species in Australia and exists all over Australia,
not just in that eastern belt that characterises the box woodlands. Being
more straight grained than E.Melliodora it has been harvested widely for
construction purposes, and originally contributed heavily to Australias
railway sleepers in the construction of railways. Along the Murray river
where it was most widespread, astronomical amounts of mature trees have
disappeared, being cleared in the wake of the food and irrigation belt,
and now more are many dying because of altered flood plains and salinity.
Unlike Yellow Box which is a tree of the high dry fertile plains, River
Red Gum is a tree of rivers and flood plains. Its heavy red timber is
ideally suited to heavy construction.
are heavy honey producers, and Yellow Box honey is one of the finest honeys
already mentioned the slow growth rate which has contributed to Yellow
Boxs inability to compete in regeneration particularly when
this is combined with the introduction of choking exotic plant species
and the tendency to be prone to devastating insect attacks which set it
back even further when they dont kill it. Once upon a time the insects
would have killed off a certain quota, leaving others to continue to grow.
Now there are fewer yellow box trees regenerating and the pests have less
to choose from. More are prone to various degrees of blight.
River Red Gum on the other hand is a relatively robust tree and a relatively
fast grower. It is more sensitive to fire than Yellow Box (it has no lignotuber
and does not regenerate easily after a fierce bushfire) but all in all,
is a more disease resistant tree. It is also more frost prone than the
frost resistant box trees, but again, it shows great variation within
the species, and River Red Gums from some areas (such as Victoria for
instance) are more cold resistant than River Red Gums growing elsewhere
(such as the Northern Territory).
I was experimenting growing River Red Gum in an extremely cold area (near
Canberra, which is not its native habitat) and these particular
trees which came from Victoria proved remarkably successful. One grew
7 metres tall and 5 metres wide (it had a remarkably leafy and wide crown)
in 10 years. For all its setbacks suffered in an inordinately cold climate,
it grew remarkably quickly. It was from this tree I took seed and discovered
it had hybridised with the locally native (but dying) Yellow Box trees.
been the Australian hardwoods that were most taken for granted and seen
as an infinite resource, which now is no more. They were burnt and still
are, widely, with their slow, hot burning timber being prized for fuel.
The timber, being hard to work, was substituted for Radiata Pine in the
building industry, but nothing can replace hardwoods durability
and termite resistance. Softer timber eucalypts are sought after for the
pulpwood and paper industry, and heavy timber railway sleepers have been
replaced by concrete ones. We still however, chose to build our house
out of Australian hardwoods (even recycled bridge timbers) and though
the construction was slower and required heavy power tools, the result
is one that is more durable and pleasing. When dressed and polished, the
dense grained hardwoods are excellent for funiture making, exposed building
timbers and other purposes. I would like to believe that the heavy hardwoods
are there for future generations. In inadvertently crossing Yellow Box
and River Red Gum , I hopefully also have some good honey producing hybrids
growing. Time will tell.
I have growing on our land are growing in the most adverse conditions
possible, suffering about 5 months of frosts a year, and bitterly cold
winds. I am sure they would be growing faster in more optimum conditions.
Nine were planted in 1994 and all nine are alive and thriving. I intend
to generate some more. So far, they have displayed what is called hybrid
vigour. They look like a disease resistant version of a young Yellow Box
(see photo below) but grow at a rate comparable to a River Red Gum. Notice
the photo is of a young hybrid growing next to a control River Red Gum
and they are of comparable growth rates, about five feet in six years,
which I admit is not fast, but which Im sure would be increased
in a more hospitable climate. Both require relatively fertile, or at least
clayey soils. I expect that like its parents, the hybrid will not be a
backyard tree, as both trees are large, growing to at least thirty metres
I am particularly interested in keeping the Yellow Box genes alive and
would hate to see the demise of this beautiful and useful tree.
(left) grows comparably to young River Red Gum (right). Both were
planted in 1994 as seedlings from the same parent River Red Gum
tree and are growing well under adverse conditions. The hybrid,
unlike its River Red Gum parent, has a lignotuber.